Chlamydia are gram-negative bacterial pathogens that infect a wide range of hosts and cause various diseases, including preventable blindness in developing countries, sexually transmitted disease and pneumonia. Chlamydia invade cells and replicate within a membrane-bound compartment, named the inclusion, that potentially serves as a protector shield against immune surveillance and also acts as a "filter" to exchange factors with the host cell. Despite the primary importance of Chlamydia as a human pathogen, little is known about the bacterial and host factors involved in the infection process. This paucity of knowledge is mainly due to the fact that Chlamydia is not a genetically tractable organism and to the difficulty of conducting genetic approaches in the mammalian host. [unreadable] To further get insights into the mechanisms involved in Chlamydia pathogenesis, we have developed a genetic approach in the model organism Drosophila melanogaster. We have shown that Drosophila SL2 cells constitute a viable model to study Chlamydia infection. We demonstrated that, similar to the situation in mammalian cells, infectious forms (EB) of C. caviae, the guinea pig model of genital and ocular infection of C. trachomatis, enter Drosophila SL2 cells, differentiate into the replicative form (RB), replicate within a membrane-bound compartment and differentiate back from RBs to EBs. Using this model system, we have performed a genome wide RNAi screen and identify 450 host that when depleted increased or decreased C. caviae intracellular growth. We now propose: (1) to confirm the candidates identified in the primary screen, (2) to identify the host factors specifically involved in Chlamydia infection, (3) to validate the selected Chlamydia-specific candidates in a mammalian system. Altogether, our genetic approach should lead to the identification of uncovered host factors involved in Chlamydia pathogenesis. Our long-term goal is to characterize the function of the identified candidates in order to better understand the complex interaction between Chlamydia and its host and potentially identify novel targets for therapeutic treatment. [unreadable] [unreadable] [unreadable] [unreadable]